According to a paediatrician and a medical anthropology professor, the “epidemic” increase in chronic, hard-to-diagnose childhood problems, such as allergies, asthma, autism and ADHD, can be attributed to diet.

In their new book What’s Making Our Children Sick?, Dr Michelle Perro and Professor Vincanne Adams claim that unless children are eating 100 per cent organic food or home-grown veg, they are eating “toxic ingredients” like pesticides, hormones and antibiotics that are harmful to their health.

They claim a broad spectrum of childhood illnesses can be tied to exposure to food and environment.

The illnesses include basic digestive disorders from reflux and constipation to colitis, immune disorders such as allergies and asthma, and neurocognitive disorders such as autism, ADHD and various mood disorders.

They say obesity, diabetes and other endocrine issues can also be related to the food supply and exposure to environmental endocrine disruptors.

Perro, a former director of the paediatric emergency department at New York’s Metropolitan Hospital, said: “There are other concerns that are not as well-publicised but are equally troublesome, such as sleep disorders and fatigue. Many kids just don't feel well.”

Some health problems have become more prevalent in UK children. Allergy UK say the percentage of children with allergic conditions has risen dramatically.

Childhood cases of eczema and hayfever have trebled in the last 30 years, and the prevalence of kids with a peanut allergy has doubled in 10 years in western nations.

In addition, in the five years to 2012 the number of children classed as being autistic in the UK rose by more than 50 per cent.

Although many factors are linked to chronic illnesses in children, Perro and Adams focus on what they say is one of the biggest causes – industrialised food.

They say weed and insect resistance has led to “alarming” increases in pesticides in food.

The most significant increase, they claim, has been in the use of glyphosate-based herbicides and more toxic formulations of new pesticides.

Adams said: “Foods once considered ‘healthy’ are now potentially full of toxicants that are causing systemic issues in our children’s guts.”

She said that while there are no good studies of the effects of these foods in humans, animal studies point to major concerns.

They include disruptions of the microbiome, leaky gut and dysbiosis (an imbalance between good bacteria and bad bacteria in the gut) that can lead to malfunctioning immune systems and inflamed brains.

There are many factors beyond food that may be involved in poor childhood health, say Perro and Adams, including toxins and toxicants such as plastics, flame-retardants, air pollution and chemicals from cleaning products, plus stress.

Adams, a professor at the University of California in San Francisco, said: “The tools of medicine have not caught up with the kinds of pathogens kids are exposed to.